Amid Corn Belt-wide rains and cooler northern Illinois weather throughout April and May, there may be a small silver lining: Soilborne larvae and eggs often don’t thrive in saturated, cold soils.
“It depends on how the weather progresses,” says Kelly Estes, Illinois agricultural pest survey coordinator. “Toward the end of May, we get rootworm hatch. If we have a lot of wet, soggy conditions for that hatch, farmers who have them on their acreage may get lucky.”
When asked how freezes over the winter might affect Japanese beetles, Estes says much of the population is strongly adapted and likely “came through,” though she’s unsure how rain will impact the population ahead of adult beetle emergence in the middle of summer.
The pest has been a growing concern for western Illinois, with an 11-county northwestern region averaging 175 Japanese beetles per 100 sweeps in 2018. The statewide average in 2017 was 28, according to the Illinois pest survey.
Delayed planting caused by rain is particularly severe in Illinois, which means reports of early-season insects that target seeds or crops in early growth stages are few and far between. As early emergers, from slugs to grubs to May beetles, have cropped up, Estes says many of their “breakfasts,” or seeds, weren’t waiting for them.
“Whether or not slugs become an issue depends on whether or not it’s still wet when these late-planted crops are starting to develop — especially when they’re germinating,” adds Nick Seiter, a University of Illinois entomologist. “When you have the wet conditions at the same time, that’s where slugs can be an issue.”
Black cutworm had a large impact in May 2018, with significant and sustained flights of the moth coming up until the end of the month. Estes says so far in 2019, according to her group’s traps, there have been fewer black cutworm flights than last year.
“If we were to be in a situation like that again this year, with flights continuing through the end of May — with planting beans so far pushed back and smaller corn — the threat of feeding and cutting could be high if we get those numbers again,” Estes says.
True armyworm has been appearing in wheat fields because moths are attracted to areas with green cover, Estes says. In 2019, more acres in Illinois are cover cropped than years past, which also brought the worm to stands that are being tilled or sprayed to make room for a cash crop.
“There again, a lot of late-planted corn is susceptible to true armyworm, so farmers should be keeping an eye out,” she says.
Seiter says farmers in Illinois may want to watch for dectes stem borer, a soybean pest that can be identified by petioles on leaves in late June. The pest eventually bores down to the stem and only causes yield loss when harvest is delayed, as the longer the borer stays lodged at the bottom of the plant before harvest, the more likely it is that lodging will occur.
“We saw a lot of that last fall, particularly in southern Illinois with delays in harvest from the weather,” Seiter says. “When you have that delay combined with dectes stem borer, you can see increases in lodging, and of course, that delay in harvest can cause some lodging problems anyway.”